Generally, in disc brakes, the brake caliper is arranged astride of the outer peripheral edge of a brake disc. The brake caliper usually comprises a body having two elongated elements that are arranged so as to face opposite braking surfaces of a disc. Between each elongated element of the caliper and the braking surfaces of the brake disc there are friction pads. At least one of the elongated elements of the body of the caliper has cylinders suitable for receiving hydraulic pistons capable of exerting a thrusting action on the pads, abutting them against the braking surfaces of the disc to exert a braking action on the vehicle.
The brake calipers are usually fixedly connected to a support structure that remains fixed to the vehicle, like for example an axle-journal of a vehicle's suspension.
In a typical arrangement, one of the two elongated elements has two or more attachment portions of the body of the caliper to the support structure, for example providing slots or eyelets, for example arranged axially, or through holes, for example arranged radially, suitable for receiving screws for fixing the caliper that, with their ends are received in threaded holes provided on the support of the caliper.
In a typical construction of a caliper body, the elongated elements arranged facing the braking surfaces of the disc are connected together by bridge elements arranged astride of the disc.
A caliper body of this type is described in EP-A-2022999. FIG. 1 of EP-A-2022999 shows a caliper body of the fixed caliper type. This caliper body is of the monoblock type comprising two elongated elements the ends of which are connected together by bridges. Stiffening shafts extend between the elongated elements and between the two bridges forming a cross structure.
Typically, the body of the caliper is made from metal like for example aluminium, or aluminium alloy or cast iron. The body of the caliper can be obtained by casting, but also by chip-removal machining, as well as by forging.
The body of the caliper can be produced in a single piece or monoblock, but also in two half-calipers typically connected together along a plane that usually coincides with a middle plane of the disc on which the caliper is arranged astride.
In the case in which the driver of an automobile wishes to brake or slow down the movement of the vehicle, he applies a force on the brake pedal. Such a force on the brake pedal, through a brake pump, exerts a pressure on the brake fluid that, through a duct, is applied to the brake fluid present in the hydraulic circuit arranged inside the body of the caliper until the cylinders are reached where the pressure is exerted on the surface of the bottom of the pistons, forcing them to clamp against the pads that, in turn, abut against the braking surfaces of the disc.
The pressure action of the brake fluid also acts on the bottom wall of the cylinder causing a reaction in the caliper body that axially deforms it away from the surfaces of the disc. This deformation of the caliper body leads to an increase in the stroke of the pistons and therefore to an increase in the stroke of the brake pedal.
The body of the caliper also deforms as a function of the torque, exerted by the action of the pistons that abut the pads against the braking surfaces of the disc, which applies a deformation moment in directions that form torque arms with respect to the attachment points of the caliper body to its support. Such a torque deforms the caliper body also in a tangential and radial direction with respect to the disc.
Moreover, in cases in which the caliper body comprises two half-calipers, a high tension zone is created at the joining plane of the two half-calipers, which, as stated earlier, usually coincides with the middle plane of the disc on which the caliper is arranged astride.
At such a middle plane, both in monoblock caliper bodies and in caliper bodies comprising two half-calipers, there is a build-up of the tensions due to the aforementioned torque effects and the tensions generated by the pressure of the pads i.e. by the axial deformation. In the case of caliper bodies comprising two half-bodies, these tensions are added to by the tension caused by the screw tightening at the same plane. In other words, the screw that joins the two half-calipers generates a pulling tension at the joining plane of the two half-calipers that adds to the aforementioned tensions, creating a critical zone.
The caliper body must therefore have a sufficient structural rigidity, so as to ensure that the deformation of the caliper body caused by the braking action is kept within tolerable values, so as to avoid damaging the braking system and not to give the driver the feeling of having a non-responsive braking system, determining an extra stroke of the lever or pedal of the braking system and creating a feeling of a “spongy” system. This requirement pushes towards having extremely rigid structures for the caliper bodies and thus increasing their bulk and weight, especially in the most critical areas.
On the other hand, the caliper body, being fixedly connected to the vehicle's suspension and being arranged astride of the disc, is one of the non-suspended masses that it is wished to reduce as much as possible to increase the performance of the vehicle.
Such considerations are extremely important when the vehicle is a racing vehicle and the user wishes to have a braking system that is extremely responsive to his commands and at the same time is extremely light so as not to penalise the performance of the racing vehicle.
There is therefore a need for a caliper body for a disc brake that has improved structural characteristics for the same weight of the caliper body, or else one with the same structural characteristics that is lighter than the solutions of the prior art.
There are known solutions for caliper bodies specially studied to increase the characteristics of structural rigidity. For example, the aforementioned patent application EP-A-2022999, international patent application PCT/EP2005/050615 and American patent U.S. Pat. No. 3,183,999 all have solutions for caliper bodies equipped with reinforcement elements, for example arranged around the caliper bodies. In some of these known solutions the caliper body is of the symmetrical type according to planes passing through the axis of the disc or through the middle of the disc. In other solutions the caliper body has large and distributed windows, possibly passing right through, which form elongated reinforcement elements arranged longitudinally to the caliper body.
Although satisfactory from various points of view, these known solutions do not allow achieving structures that maximise the structural rigidity of the caliper body, reducing its weight and at the same time keeping the bulk as low as possible so as to facilitate the mounting of the caliper body also inside rims and wheels on which brake discs having a large diameter are mounted.